The main components of automatic transmissions are conventional, as are manually operated gear mechanisms, wherein the shifting and/or starting clutch between the driving motor and transmission, as well as the selection and shifting of gears, are actuated automatically using corresponding operating elements. These operating elements are typically configured as hydraulic or pneumatic actuating cylinders or as electric actuators, which act upon actuating devices for the above gear functions. The actuating devices can be provided on or in the transmission.
For the actuation of hydraulic or pneumatic operating elements, pressure-generating and control devices are required which, according to the state of the art, comprise a hydraulic or pneumatic pump as the pressure-generating device, a pressure accumulator, a hydraulic or pneumatic control unit with control valves and sensors, which are connected to a central control and regulating device, and can be actuated by the same, based on control and regulating functions stored there.
For cost reasons and to minimize the complexity of an actuating element, it is frequently undesirable to provide a separate pressure sensor for determining the actuating pressure of an actuating cylinder.
DE 101 31 853 A1 describes a method for determining the actuation pressure of a positioning cylinder operated by fluid pressure. This method uses only one pressure sensor for determining the actuation pressure. This pressure sensor is located between a main shut-off valve and control valves for actuating the actuating cylinder and, depending on the positions of the valves of the actuating element, can sense different pressures, for example the inflow pressure from the pressure supply system or a pressure comparable to the actuating pressure of the actuating cylinder. By applying an actuating pressure on the actuating cylinder, the cylinder is displaced. The displacement can be obtained from an existing signal, for example the signal of a displacement sensor integrated in the actuating cylinder or attached externally. The actuating pressure of the actuating cylinder is determined by computation from the inflow pressure detected by the pressure sensor, using the change in travel effected by the actuating pressure. Compared to other known methods also using only one pressure sensor, this method achieves greater accuracy for determining the actuating pressure and hence the actuating force of an actuating cylinder operated by pressurized medium.
It is the object of the invention to provide a method for determining an actuating pressure of an operating element, according to which the actuating pressure is determined without the use of a pressure sensor.